Numerous appliances having a function of connecting to a home network have been commercially available in recent years. A user can, for example, operate such appliances via the network using this function. However, when the communication via the network is interrupted for some reason, the user loses the ability to operate the appliances via the network. To address this concern, techniques for detecting the communication interruption to recognize the inoperability of the appliances have been proposed (see, for example, Patent Literature 1).